Code:
db_query("insert into $sql_tbl[customers] (login,usertype,membership,password,password_hint,password_hint_answer,title,firstname,lastname,company,b_address,b_city,b_state,b_country,b_zipcode,s_address,s_city,s_state,s_country,s_zipcode,phone,email,fax,url,card_name,card_type,card_number,card_expire,card_cvv2,first_login,status,referer,pending_membership,ssn) values ('$uname','$usertype','".@$membership."','$crypted','".@$password_hint."','".@$password_hint_answer."','$title','$firstname','$lastname','$company','$b_address','$b_city','$b_state','$b_country','$b_zipcode','$s_address','$s_city','$s_state','$s_country','$s_zipcode','$phone','$email','$fax','$url','".@$card_name."','".@$card_type."','".text_crypt(@$card_number)."','".@$card_expire."','".@$card_cvv2."','".time()."','Y','".@$RefererCookie."','".@$pending_membership."','".@$ssn."')");
You would need to alter the table to have news rows for those 2 or 4 fields if your using the s_ ones as well.
X-cart assumes that the firstname and lastname will be the same for all of them so it only stores them as firstname,lastname
You could either have it store them as those, by changing your forms, or alter the table and change the insert query.